PostCrows
A DIY beam-splitter teleprompter puts your script directly on the camera’s optical axis, so you read and look down the lens at the same time. Built from a sheet of beam-splitter glass, a box to hold it at 45 degrees and the phone you already own, it costs roughly $40 to $60 and takes an afternoon. The result is the same eyeline broadcast studios use.
This is the one piece of teleprompter gear worth building rather than buying, because the commercial versions are mostly the same parts with a bracket.
How does a beam-splitter teleprompter work?
A half-silvered mirror sits at 45 degrees in front of the lens. It passes most light through to the camera and reflects some back toward you. You see your script in the glass; the camera sees straight through it to your face.
Because the script is reflected, it has to be flipped horizontally on the screen, which is what mirror mode does. Without it the camera is fine but your text reads backwards.
The takeaway: the glass reflects the script to you and passes your face to the camera, so the text must be mirrored on screen.
What do you need?
| Part | Rough cost | Notes |
|---|---|---|
| Beam-splitter glass, 30/70 or 50/50 | $25 to $40 | The only part worth buying properly |
| Foam board or thin plywood | $5 | For the hood and frame |
| Gaffer tape or small hinges | $5 | Gaffer is fine and reversible |
| Phone or tablet | Already owned | Runs the prompter |
| Tripod | Already owned | Holds the camera, not the rig |
Do not substitute a picture frame or acrylic sheet for the glass. Ordinary glass reflects too little and produces a double image from its two surfaces, which shows up as ghosting on the text. Beam-splitter glass is coated on one side specifically to avoid this, and it is the reason the build works at all.
A 30/70 split (30 percent reflected, 70 percent transmitted) loses you about half a stop of light and gives a clearly readable reflection. A 50/50 gives a brighter script and costs a full stop. If you shoot in decent light, 30/70 is the better trade.
How do you build it?
- Cut the base. A rectangle of foam board slightly wider than your phone, with a lip at the front to stop the glass sliding.
- Mount the glass at 45 degrees. Two triangular side pieces cut at 45 degrees, glass taped into the slot between them. Accuracy here matters more than neatness: a few degrees off and the text sits high or low in frame.
- Lay the phone flat, screen up, under the glass. The screen reflects up into it.
- Build a hood. A three-sided box of black foam board over the glass, open toward you. This is not optional. Without it, room light washes the reflection out and the script becomes unreadable.
- Cut a hole for the lens. In the back panel, behind the glass, sized to your lens barrel.
- Turn on mirror mode in the prompter and check the text reads correctly in the glass.
The takeaway: the two steps people get wrong are the 45 degree angle and skipping the hood.
How do you line it up with the camera?
Put the camera behind the glass with the lens as close to it as it will physically go. The nearer the lens is, the less of the frame edge picks up the glass border.
Three checks before you record:
- Look through the viewfinder for glass edges. If a frame edge is visible, move the camera closer or crop slightly in post.
- Check for reflections of your own gear. A bright laptop or a window behind the camera will show up in the glass. Black foam board or a dark cloth behind the rig kills it.
- Check the text sits at lens height. If you are reading noticeably above or below the lens, the 45 degree angle is off.
What settings should the prompter use?
Different from reading off a bare screen, because the glass is further from your face and dimmer:
- Mirror mode on. Always, for glass.
- Fewer words per line. About 3 to 5, rather than the 6 to 8 that suits arm’s length.
- Larger text. You are reading a reflection, not the screen.
- High contrast. White on black reflects far better than anything else. Coloured themes look good on a screen and poor in glass.
- Maximum screen brightness. The glass is throwing away 70 percent of your light.
The takeaway: mirror on, bigger text, fewer words per line, white on black, brightness up.
Is it worth building versus buying?
A commercial phone-sized beam-splitter rig runs roughly $80 to $200. The glass inside is the same component you would buy for $25 to $40.
Build it if you want to understand the geometry, you have an unusual camera or phone size, or you would rather spend the difference on light. Buy it if you need it to fold down and survive being carried, since a foam board rig does not travel well.
Either way, the prompter software is the same and the settings above do not change.
Troubleshooting
- Ghosted or doubled text. You are using ordinary glass or acrylic. Only beam-splitter glass fixes this.
- Washed out script. The hood is missing or too shallow. Extend it.
- Text too high or low in the glass. The 45 degree angle is off. Re-cut the side pieces.
- Reflections of the room. Something bright is behind the camera. Black it out.
- Dark footage. Expected: you are losing half a stop to a stop. Add light rather than raising ISO.
What to do next
Build the frame from foam board first and test with tape before cutting anything permanent. The angle is the only measurement that has to be right, and you will want to adjust it once you see the text in the glass.
Then set the prompter to mirror, white on black, 3 to 5 words a line, and record fifteen seconds to check the eyeline.